The 2004 Oct. 28 and Nov. 2 flares were the most prolific
emitters of nuclear gamma-rays observed by {\em RHESSI},
with measured fluences >1900 and ~ 900 \gamma
cm-2, respectively. The Oct. 28 event was the brightest
gamma-ray flare detected in over 20 years. We discuss
measurements of nuclear de-excitation lines from Fe, Mg, Ne,
Si, C, and O that provide information on the directionality
of accelerated particles and the composition of the flare
plasma where they interact. A strong narrow \gamma-ray
line is emitted when neutrons produced by similar
interactions are captured in the photosphere by H. We have
imaged this capture-line and resolved a double source with
components located on opposite sides of the post-flare
arcade observed by {\em TRACE} in the Oct. 28 flare. We also
discuss {\em RHESSI} images of the Oct. 29 and Nov. 2
flares. The positron-electron annihilation line and
continuum provide information on the temperature and density
near where the ions interact. The 511 keV line observed by
{\em RHESSI} in the 2002 July 23 flare had a Gaussian width
of 8.1 ± 1.1 keV FWHM, consistent with ~(4-7)
\times 105K, if the broadening is thermal. The
annihilation lines observed early in the Oct. 28 and Nov. 2
flares are also broadened: ~5.5 and ~6.5 keV
FWHM, respectively. The lack of a strong positronium
continuum suggests that the lines are broadened thermally in
an ionized medium at ~1014 H cm-3. The line
narrows significantly to ~1 keV later in the Oct. 28
flare, suggestive of a significant drop in temperature. This
work was supported by NASA DPR W19746/10049 at NRL and by
NAS 5-98033 at UCB and GSFC.

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